The proposed research is intended to investigate the hypothesis that early experiential influence on adult aggression is in part a function of factors working to modulate the excitability of restricted limbic circuits to a variety of inputs. Previous work (Adamec, Ph.D. Thesis, McGill University, 1973) has suggested that measures of epileptic excitability of the amygdala, and its projection field, are closely related to the behavioral manifestations of the prolonged inhibitory influence exerted by the amygdala on feline predatory aggression. Increasing the epileptic excitability of the amygdaloid system with electrical stimulation suppresses attack in cats permanently and leads to enhanced aggressive-defensive conflicts like those seen in naturally non-aggressive cats. This brain-behavior relationship has only been investigated in adult cats. From naturalistic observations there are reasons to believe that certain types of early experience known to influence predatory aggression operate upon defensive behaviors which are probably modulated by the amygdala. This project, therefore, will manipulate feline early experience and trace behaviorally the development of aggressive- defensive conflicts into adulthood. Measures of limbic neural response to both epileptic and non-epileptic inputs will then be taken, and related to juvenile and adult measures of aggressive-defensive conflicts with predatory and non-predatory contexts. These investigations have two main objectives. The first is to establish a link between early experiential influence on adult aggression and excitability of limbic circuits functioning to enhance aggressive- defensive conflicts. Since most measures of limbic excitability used thus far have involved electrical stimulation of after-discharges a second objective is to relate as closely as possible these epileptic measures to more physiologically "normal" measures of neural excitability. These non-epileptic measures will include recording of limbic multi-unit activity in response to natural prey and conspecific threat stimuli, and analysis of electrically evoked potentials with the amygdaloid projection field.